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December 15, 2010
Chiral What? Chiral How?
Thanks to an email from a reader, I can bring you this very weird paper from Tetrahedron. The authors claim to have extracted a local plant and isolated nevirapine, (sold as Viramune by Boehringer Ingleheim as a reverse transcriptase inhibitor for HIV).
That's kind of odd. I'm no natural products expert, but I've sure seen a lot of them over the years, and that framework (and the N-cyclopropyl) don't look so likely to me. But hey, plants do odd things. That's not what's really puzzling about this paper. No, what's had me staring at it this morning is the claim that, in contrast to the marketed drug, this stuff is optically active nevirapine.
Say what? Try as I might, I can't see any plausible way that that's a chiral compound. The authors seem to think it is, though. They claim optical rotation, somehow, and then say that "The detailed structure and stereochemistry of compound 1 was established unambiguously by single crystal X-ray crystallography." But hold on - that's not as easy as it sounds. Getting absolute configurations from the X-ray data of light-atom-only molecules takes special efforts, and I don't see any being taken (molybdenum X-rays, direct methods, no talk of anomalous dispersion, etc.)
I'm just not willing to see that nitrogen atom as a source of chirality - if it were, shouldn't that be the focus of this whole paper? Instead, the authors just blithely tell us how neat it is that they've isolated the chiral material. In fact, they find it so neat that they tell us two times in a row:
This is a very interesting discovery that naturally occurring optically active nevirapine has been biosynthesized in the seeds of C.viscosa and the optically inactive nevirapine was designed as a selective non-nucleoside inhibitor of HIV-1 reverse transcriptase. It is also a remarkable ﬁnding that the seed of C.viscosa is the source of optically active nevirapine, which was also designed and synthesized before its isolation from natural source.
This sounds like some sort of lunatic patent-busting exercise, to be honest. And it sounds as if someone doesn't know what a chiral compound is. And that whoever reviewed this for Tetrahedron was incompetent. And that the editor who let it through should be a least a little bit ashamed. Well?
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